1. Field of the Invention
This invention relates to filter elements, and more particularly, to filter elements used in backflushable filter units wherein the filters suffer from premature failure due to the filtering-cleaning cycle imposed thereon. The invention comprehends a means for limiting this premature failure by incorporating a novel support system during the manufacturing of the filter.
2. Background of the Prior Art
The U.S. Pat. No. 3,994,810, a backflushable filter unit having a plurality of filter elements is taught. The filter elements therein are depicted as being cylindrical with pleated filter media being secured to the end caps of the filter elements. The prefered filter media for filtering polymers is mentioned as a metal fiber depth filter media wherein the metal fibers have a diameter from about 1 micron to about 50 microns and the media is sintered.
Generally, in the operation of filter units and including backflushable units, the flow of contaminated fluid is usually from outside the filter element into the center of the element and then out through the center of the filter housing. However, in backflushable filter units, the flow is preselectedly reversed so that some of the clean fluid is used for flowing from inside the filter element to its outside thereby cleaning it.
In such backflushable filter units, the filters are on-stream filtering for a preselected period of time and then selectively switched off-stream either individually or in pairs being cleaned for a preselected period of time. The cleaning period or time required to clean the filters is dependent upon:
(1) How dirty the filters are; PA1 (2) The type of fluid in the system; PA1 (3) The type of contaminants; PA1 (4) The amount of pressure drop in the device; and PA1 (5) The desired level of cleanness.
The filtering and cleaning causes the pleated filter media of the filter elements to be subjected to a cyclic pressure effect. It has been found that under certain circumstances, such as a high differential pressure across the filter media and a high viscosity liquid being filtered, that the crowns of the pleats of some of the elements in a backflushable unit were cracking or splitting such as depicted in the photograph of FIG. 1.
It was initially believed that this splitting of the crowns was due to failure of the fastening means that was used to attach the pleated filter media to the end caps. A number of such filter elements were made in accordance with U.S. Pat. No. 4,169,059 wherein a metal fiber web is used as means for bonding the filter media to the end caps. An extensive evaluation of a plurality of such filter elements, such as those depicted in FIG. 1, indicated that the bonding means for securing the pleated filter media to the end caps was fully intact. And, thus, bonding failure was not the cause of the splitting of the crowns. Therefore, the obvious solution, making the bond stronger, would not prevent the splitting.
Thus, recognition of the splits in the crowns and the review of the prior art did not lead one to any conclusion as to how to solve the splitting problem.